The Advanced Television Systems Committee Vestigial Sideband (ATSC VSB), U.S-oriented terrestrial waves digital broadcasting system, is a single carrier scheme and uses field synchronizing signal by 312 segment unit. Accordingly, reception performance is not good in poor channels, especially in a doppler fading channel.
FIG. 1 is a block diagram showing a conventional transmitter of the ATSC VSB. The digital broadcasting transmitter of FIG. 1, which is an Enhanced Vestigial Sideband (EVSB) system proposed by Philips, forms and transmits a dual stream by adding a robust data to a normal data of the existing ATSC VSB system.
As shown in FIG. 1, the digital broadcasting transmitter has a randomizer (11) for randomizing data, a first RS encoder (12) for performing RS encoding of the randomized data, a packet formatter (13) for interleaving the robust data of the encoded data, restructuring a packet at ½ rate, inserting a packet identifier (PID) and multiplexing the data with the normal data, an interleaver (14) for interleaving the data, a Trellis encoder (15) for performing enhanced coding and then the general ⅔ rate Trellis encoding of the robust data of the interleaved data, a controller (16) for outputting a signal to control the normal data and robust data, a second RS encoder (17) for performing RS re-encoding of the enhanced-coded robust data to be compatible with the existing receiver and replacing parity, a multiplexer (18) for inserting field sync and segment sync in the Trellis-coded data, and a modulator (19) for adding a pilot to the multiplexed signal and carrying out Vestigial Sideband (VSB) modulation and RF upconverting.
Referring to FIG. 1, the normal data and robust data are multiplexed (not shown) according to the dual stream scheme which transmits the normal data and robust data in one channel and the multiplexed data are input to the randomizer (11). The input data are randomized by the randomizer (11), input to the first RS encoder (12), RS encoded to correct channel-generated errors, and input to the packet formatter (13). Then the robust processing is performed such that the robust data of the encoded data are interleaved, restructured with packet at ½ rate and inserted with the PID. The data after the robust processing are then multiplexed with the normal data and output.
FIG. 2 shows a data format output from the packet formatter (13) of FIG. 1.
Referring to FIG. 2, the normal data and robust data are arranged at certain intervals so that the normal signal and robust signal after Trellis encoding are distributed at regular intervals.
The resultant output data are interleaved through the interleaver (14) which disperses the data, the robust data are enhanced-coded, and the data are Trellis-encoded through the Trellis encoder (15) which performs the general ⅔ rate Trellis encoding. The enhanced-coded robust data are RS re-encoded to be compatible with the existing receiver and the parity is sent to the Trellis encoder (15) through the second RS encoder (17) which replaces the parity. The signal passes through the multiplexer (18) which inserts the field sync and segment sync in the Trellis-encoded data, and is sent to the modulator (19) which adds pilot and performs VSB modulation and RF upconverting with respect to the signal, and then transmitted. Here, the normal data and robust data are controlled by the controller (16) which outputs a signal to control the normal data and robust data.
The U.S-oriented terrestrial waves digital television system of FIG. 1 is constructed to form a dual stream by adding the robust data in the normal data of the existing ATSC VSB system and transmit the dual stream, so that the existing normal data and the robust data are transmitted altogether.
However, the U.S-oriented terrestrial waves digital television system of FIG. 1 has a problem that in spite of transmitting the dual stream with the robust data added, poor transmission performance at multipath channels due to transmission of the existing normal stream is almost not improved. In other words, the improved normal stream rarely improves reception performance and the robust stream has no remarkable effect on reception performance in the multipath environment.